mfd: stmpe: Switch to using gpiod API

This patch switches the driver away from legacy gpio/of_gpio API to
gpiod API, and removes use of of_get_named_gpio_flags() which I want to
make private to gpiolib.

We also need to patch relevant DTS files, as the original code relied on
the fact that of_get_named_gpio_flags() would fetch any data encoded in
GPIO flags, even if it does not reflect valid flags for a GPIO.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/YxeS1BK2OBH1P/kO@google.com